voltage drop 3% include transformer or not?

[binwork91]

Correct, but other codes may incorporate them as mandatory measures.

Hence my comments that 5% does not use up the entire practical voltage drop window, leaving room for some voltage drop on some transformers.


Well there you go, they are mandatory measures for you. But if they refer to "branch circuit" and "feeder" conductors, then that does not include the transformers themselves.

Cheers, Wayne

In this case, since transformer voltage drop is not considered, I guess contractors might prefer to buy high-impedance transformers because they are cheaper.

 

[binwork91]

To account for the 2-3% from the LV terminals to the Bus/load you can use the -5% tap, which means; doing the calc, voltage at the Bus/Load would be around 477.4V, very desirable on a 480V system

When use -5% tap, I get 478.4V at transformer LV terminal. Your answer is 477.4V, is it a typo? or my calculation is wrong.

Another question: When you use tap, do you recommend to adjust LV terminal to near 480V or adjust secondary OCPD to near 480V?

 

[kingpb]

13.46KV on HV side, (2.5% VD) tapped at -5%, make ratio 13.14KV/480 = 27.38. So, 13.46KV/27.38 = 491.7V on LV transformer terminals. If I use 3% VD to the load from the LV transformer terminals I get 477.4V. But not going to say my math is perfect, kind of did it quickly. I think the difference between 478.4V versus 477.4V I'd say your understanding the process.

The question regarding LV vs OCPD location. I would always try to adjust the voltage at the OCPD location close to 480V. But you need to physically measure at no-load, and make sure you are not exceeding 10% overvoltage. Not usually a problem, but does need to be checked.

 

[binwork91]

But you need to physically measure at no-load, and make sure you are not exceeding 10% overvoltage. Not usually a problem, but does need to be checked.

May I know where the 10% comes from? Is there a standard that addresses not exceeding 10% overvoltage or undervoltage?

 

[kingpb]

May I know where the 10% comes from? Is there a standard that addresses not exceeding 10% overvoltage or undervoltage?

IEEE C84.1